As a process for producing soybean oil and defatted soybean from soybean in industrial scale, a solvent extraction method which is an extraction using an organic solvent such as hexane is commonly used. When defatted soymilk is produced by water extraction of protein from soybean, a defatted soybean obtained by such a solvent extraction method is water-extracted. The resulting defatted soymilk is pasteurized and packed to provide a liquid product, or pasteurized and dried to provide a powder product. In addition, when a soybean protein isolate is produced by separating and concentrating protein from the defatted soymilk, the resulting defatted soymilk is adjusted to acidic pH to make isoelectric precipitation of protein, and the resulting precipitate is recovered and neutralized, and then pasteurized and dried to provide a powder product.
According to recent report, however, a released solvent during production is a cause of destruction of the ozone layer. In addition, even though solvent elimination of defatted soybean after a solvent extraction is carried out, a negative impression of consumers about using organic solvent as raw material of food is remained. Although a press extraction method as a safer and eco-friendly method is known, this method has a problem that it is difficult to raise the fat recovery rate than the solvent extraction method.
On the other hand, a process of separating soymilk, which is extracted from whole fat soybean, to soymilk having relatively little fat content and an emulsified composition by centrifuging the soymilk to transfer the emulsified composition (cream) having higher fat content to upper layer is considered (Patent Document 1, 2).
In addition, a process of separating off fat from soymilk by demulsifying the soymilk with demulsifier or protease is disclosed (Patent Document 3, Non-Patent Document 1). And, a process of coagulating an oil body from soybean protein by adding salts such as sodium ascorbate or sodium chloride is disclosed (Patent Document 4, 5, 6).
Further, Patent Document 7, 8 describes that soymilk having relatively little fat content and an oil body are obtained by grinding soybean with adding water, heating the ground soybean before or after separating the ground soybean to soymilk and bean curd refuse (okara), and then centrifuging the obtained soymilk at high centrifugal force.